Light antennas assemble themselves

TORONTO – New photosynthesis-inspired nanomaterials can control and direct energy absorbed from light – and can even build themselves into light-harvesting antennas.

For years, nanotechnologists have been intrigued by quantum dots, but they have not been able to build higher-order structures, or complexes, out of multiple types of these particles. The new “artificial molecules” constructed by University of Toronto researchers could fill the gap.

Combining their semiconductor and DNA experience, the team invented a generalized strategy to bind certain classes of nanoparticles together. They looked to DNA for its high degree of specificity, which enabled them to build rationally engineered designer structures out of nanomaterials, said professor Ted Sargent.

“The amazing thing is that our antennas built themselves – we coated different classes of nanoparticles with selected sequences of DNA, combined the different families in one beaker, and nature took its course,” Sargent said. “The result is a beautiful new set of self-assembled materials with exciting properties.”

Although traditional antennas increase the amount of an electromagnetic wave that is absorbed and then funnel that energy to a circuit, the new nanoantennas increase the amount of light that is absorbed and funneled into a single site within moleculelike complexes. This concept can already be seen in nature in light-harvesting antennas – constituents of leaves that make photosynthesis efficient. Here, the complexes capture the wavelengths found in sunlight, Sargent explained.

The researchers say that the concept could go beyond light antennas alone. “What this work shows is that our capacity to manipulate materials at the nanoscale is limited only by human imagination,” said professor Shana Kelley. “If semiconductor quantum dots are artificial atoms, then we have rationally synthesized artificial molecules from these versatile building blocks.”

Their research appeared in the July 10 issue of Nature Nanotechnology (doi: 10.1038/nnano.2011.100). It was supported by the Ontario Research Fund Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs program and the National Institutes of Health.

Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.